In the case where an epoxy resin composition containing a solid curing agent for epoxy resin is used as an adhesive agent or the like, the solid curing agent for epoxy resin is required to have latency good enough to keep the epoxy resin composition in a one-component state. Here, the latency is a property in which a curing agent does not act as the curing agent at a normal temperature but acts as the curing agent when heated. If the latency of the solid curing agent for epoxy resin is insufficient, the curing reaction of the epoxy resin proceeds at a normal temperature, and the viscosity of the epoxy resin composition increases. If the epoxy resin composition contains an acid anhydride or an organic solvent, the acid anhydride or the organic solvent dissolves the solid curing agent for epoxy resin and thereby causes a problem in that the latency of the solid curing agent for epoxy resin is lowered.
As a method for imparting latency to a curing agent, a method for treating a curing agent with a silane coupling agent such as y-glycidoxypropyltrimethoxysilane or with the like has been studied so far (for example, Patent Literature 1), but is still required to improve in terms of the acid anhydride resistance and the solvent resistance.
Meanwhile, in the case where a curing agent containing fine particles is treated by a dry treatment method not using a solvent, a problem has been found in that an aggregation occurs in the solid curing agent for epoxy resin.